1. Field of the Invention
The present invention relates to a color image data outputting apparatus which converts C (cyan), M (magenta), Y (yellow) and K (black) data of an image to be recorded on a sheet by an image recording apparatus into R (red), G (green) and B (blue) data and applies the RGB data to an image displaying apparatus.
2. Description of Related Art
Conventionally, systems have been available which are adapted to subject image data inputted from an image data inputting apparatus such as a scanner to various image processing operations performed by a computer and then apply the processed image data to an image recording apparatus such as a printer so as to record a desired image on a paper sheet or the like. In recent years, some of the systems have been modified so that a print-out result, which is expected to be obtained when the image is outputted on a sheet by the printer, can be checked on a display screen such as of a monitor without actually outputting the image on the sheet by the printer.
In general, printers are adapted to form an image on a sheet on the basis of subtractive-process three primary color data, i.e., C (cyan), M (magenta) and Y (yellow) data, and K (black) data, while monitors are adapted to display an image on their display screens on the basis of additive-process three primary color data, i.e., R (red), G (green) and B (blue) data. Therefore, the aforesaid system adapted to check the print-out result of the image has to convert the CMYK data of the image to be inputted to the printer into the RGB data before applying the image data to the monitor.
Where CMYK data to be outputted to a printer are converted into RGB data on a complementary color basis and then the RGB data are applied to a monitor, however, the image outputted on the monitor has a great deviation in color tone from the image outputted on a sheet because the ground color (whiteness) of the sheet is different from the whiteness of the background of the monitor display screen.
One approach to this problem is that CMYK data are converted into RGB data on the basis of correspondences between CMYK data and RGB data preliminarily determined on the basis of an absolute standard utilizing tristimulus values X, Y, Z on the XYZ color specification and then the RGB data are inputted to a monitor to display on the monitor display screen an image having the same color tone as the image to be outputted on a sheet.
More specifically, when the CMYK data are converted into the RGB data, the aforesaid prior art employs two conversion tables, i.e., a printer conversion table for converting CMYK data into data represented by tristimulus XYZ values and a monitor conversion table for converting XYZ data into RGB data.
The printer conversion table and the monitor conversion table are prepared by measuring colors of a plurality of color patches printed on a sheet by the printer and colors of a plurality of color patches displayed on the monitor display screen by means of a calorimeter. More specifically, CMYK data for predetermined plural colors (e.g., 500 to 1,000 colors) are applied to the printer, and color patches of the predetermined plural colors are printed on a predetermined sheet. Then, the colors of the color patches are each measured by the calorimeter, and correspondences between the resulting color measurement values (X, Y, Z) and the CMYK data are determined and stored in a memory. Thus, the printer conversion table for converting CMYK data into XYZ data can be obtained.
In turn, color patches respectively having colors close to the colors of the plural color patches printed on the sheet are displayed on the monitor by applying a plurality of RGB data. Then, the color of one of the color patches displayed on the monitor is measured by means of the colorimeter to obtain color measurement values (X.sub.1, Y.sub.1, Z.sub.1). At this time, the color of a color patch on the sheet close to the color of the measured color patch on the monitor is measured to obtain reference color measurement values (X, Y, Z). The corresponding RGB data to be applied to the monitor are adjusted so that the color measurement values (X.sub.1, Y.sub.1, Z.sub.1) for the color patch on the monitor display screen are equated with the reference color measurement values (X, Y, Z), i.e., the color tone of the color patch on the sheet is equated with the color tone of the color patch on the monitor display screen. The reference values (X, Y, Z) are stored in the memory in correspondence with the RGB data thus adjusted to equate the color tones of the color patches on the sheet and on the monitor with each other. This operation is performed on each of the color patches displayed on the monitor for preparation of the monitor conversion table for converting XYZ data into RGB data.
When the print-out result, which is expected to be obtained when an image is printed on a sheet by the printer, is to be displayed on the monitor display screen, the CMYK data of the image are converted into XYZ data with the use of the printer conversion table. Then, the XYZ data thus obtained are converted into RGB data with the use of the monitor conversion table. The RGB data thus obtained are inputted to the monitor. Thus, an image having the same color tone as the image to be printed on the sheet by the printer can be displayed on the monitor display screen.
Where a print-out result expected to be obtained when the image is recorded on a sheet different in paper quality (or ground color) from the sheet on which the color patches have been printed is displayed on the monitor by applying the RGB data generated on the basis of the printer conversion table and the monitor conversion table, however, the image displayed on the monitor display screen does not have the same color tone as the image to be outputted on the sheet. This is because the printer conversion table and the monitor conversion table are designed such that the correspondences between CMYK data and RGB data are determined so as to equate the color tone of an image to be printed on a sheet with the color tone of an image displayed on the monitor on the assumption that a sheet on which the image is to be printed would have the same ground color as the sheet on which the color patches have been printed.
Therefore, where the print-out result expected to be obtained when the image is printed on the sheet having a different ground color is displayed on the monitor, the prior art system requires preparation of an additional printer conversion table and a monitor conversion table. However, the preparation of these conversion tables involves the measurement of 500 to 1,000 colors as described above and, hence, requires tremendous time and labor.